In recent years, miniaturization of a semiconductor integrated circuit device has progressed. Silicon dioxide (SiO2) has been used for a gate insulation film of a transistor. However, as the miniaturization of the transistor progresses, the gate insulation film becomes thinner to such an extent that an insulation property thereof is no longer maintained due to penetration of electrons through the SiO2 film by a tunneling effect. Thus, using a High-k (high dielectric constant) material having a relative dielectric constant higher than the SiO2 material was considered. A gate insulation film having a high dielectric constant by using a High-k material has an increased effective film thickness (compared with using SiO2) to thereby break through the limit of the miniaturization caused by the tunneling effect.
The High-k material is selected from metal compounds, e.g., a metal oxide and a metal nitride. A typical High-k material is a hafnium silicate (HfSiOx).
One of the methods of forming such a HfSiOx film described in the related art includes a sequence of steps as follows:
(1) supplying a hafnium (Hf) gas (raw material gas) to form a Hf layer on a substrate;
(2) supplying an oxidizing agent gas to oxidize the Hf layer such that a HfOx (hafnium oxide) layer is formed;
(3) supplying a silicon (Si) precursor gas (raw material gas) to form a Si layer on the HfOx layer; and
(4) supplying an oxidizing agent gas to oxidize the Si layer such that a SiOx (silicon oxide) layer is formed.
By repeating the sequence of steps (1) to (4), lamination of the HfOx layer and the SiOx layer are performed. Such a lamination process is repeated until a thickness of a laminated structure reaches a designed thickness. Thus, an HfSiOx film, which is a lamination by the HfOx layer and the SiOx layer, is formed.
The High-k material represented by the HfSiOx film is expected to be used as a material of a dielectric film of a capacitor, in addition to the gate insulation film.
One method using the High-k material for the dielectric film described in the related art includes a step of simultaneously or continuously supplying a Hf precursor gas and a Si precursor gas to adsorb them onto a substrate (a first step). Although the related art describes chemical/physical absorption onto the substrate surface, not the adsorption, in a certain section thereof, the chemical absorption may have substantially the same meaning as the chemical adsorption. Further, if chemical adsorption was intended, a HfSix layer (hafnium silicide) would be formed on the substrate. The method further includes a step of supplying an oxidizing agent gas to oxidize the adsorption layer, i.e., the HfSix layer such that an HfSiOx layer is formed (a second step). By repeating the first and second steps, the HfSiOx layer is laminated. Such a lamination process is repeated until a thickness of a laminated structure which is obtained by laminating the HfSiOx layer reaches a designed thickness. Thus, an HfSiOx film is formed.
Strictly speaking, characteristic or property of the HfSiOx film varies depending on a composition ratio of Hf and Si. A variation in characteristic or property which is caused by a change in the composition ratio has been regarded as being within an acceptable range, and thus has not been a problem. However, as a reduction in thickness further progresses, even if a slight variation in characteristic or property occurs, it is remarkably seen that such a variation has a huge effect on the semiconductor integrated circuit device. Accordingly, in order to obtain an optimal characteristic or property for an intended purpose of the HfSiOx film, it is required to adjust the composition ratio of Hf and Si delicately and with a high degree of accuracy.
The first related art does not teach such a method of adjusting the composition ratio. However, in case the adjustment of the composition ratio is required, the composition ratio would be adjusted by a thickness of the Hf film that is formed in step (1) and a thickness of the Si film that is formed in step (3).
Similarly, the second related art does not teach the method of adjusting the composition ratio, either. However, in case adjusting the composition ratio is required, the composition ratio would be adjusted by the amount of each of the Hf raw material gas and the Si raw material gas, which are supplied in step (1).
In the case where the HfSiOx film is used as the gate insulation film and the capacitor dielectric film, which are required to have a further reduced thickness, the composition ratio of Hf and Si is occasionally required to be drastically adjusted.
Obtaining a Hf-rich HfSiOx film having the composition ratio of Hf:Si, e.g., 90:10 to 95:5 is an example of such a case. In obtaining the HfSiOx film like this, the laminating of the HfOx layer and the SiOx layer as described in the first related art has problems in that the composition ratio of Hf and Si is limited by a growth rate of the Si film. Further, under a thin film thickness condition, it may be difficult to obtain the desired composition ratio. Let's suppose that a formable minimum thickness of the Si film is, e.g., lnm. Then, when the composition ratio of Hf and Si is 90:10, the Hf film needs to have a film thickness of 9 nm.
In other words, in the method of laminating the HfOx layer and the SiOx layer, the formation of the HfSiOx film, in which the composition ratio of Hf and Si is 90:10, has a limitation in thickness of approximately 10 nm (1 nm+9 nm). In addition, when the composition ratio of Hf and Si is 95:5, a required thickness of the Hf film is 19 nm. As a result, the formation of the HfSiOx film, in which the composition ratio of Hf and Si is 95:5, has a limitation in thickness of approximately 20 nm (1 nm+19 nm).
In the method of laminating the HfSiOx layer as described in the second related art, a proportion of Hf is decreased while that of Si is increased when wafer temperature is increased. According to the second related art, when the wafer temperature is 350 degrees C., the proportions of Hf and Si atoms in the HfSiOx film are 20.3% and 10.9%, respectively, whereas when the wafer temperature is 400 degrees C., the proportions of Hf and Si atoms in the HfSiOx film are 18.5% and 13.3%, respectively. As described above, in the method of laminating the HfSiOx layer, there is a tendency that the proportion of Hf is decreased and that of Si is increased along with the increase in wafer temperature. This makes it difficult to significantly increase the proportion of Hf to Si, thus resulting in a deteriorated flexibility for adjustment of the composition ratio. Further, in the second related art, the oxidizing process is repeated in each supply of the Hf precursor gas and the Si precursor gas. This makes it difficult to obtain the Hf-rich HfSiOx film having, e.g., the composition ratio of Hf:Si=90:10 to 95:5.